U.S. patent number 8,615,126 [Application Number 13/170,126] was granted by the patent office on 2013-12-24 for method for performing pattern decomposition based on feature pitch.
This patent grant is currently assigned to ASML Masktools B.V.. The grantee listed for this patent is Jung Chul Park. Invention is credited to Jung Chul Park.
United States Patent |
8,615,126 |
Park |
December 24, 2013 |
Method for performing pattern decomposition based on feature
pitch
Abstract
The present invention discloses a method for decomposing a
target pattern containing features to be printed on a wafer, into
multiple patterns, the features having a plurality of patterns
within a minimum pitch for processes utilized to image the target
pattern. The method includes superposing a predefined kernel over a
pixel, and moving the kernel from one pixel to another, the pixels
representing the sub-patterns of the target pattern. Polarity of
the kernel may be reversed when the pixel has a stored intensity
value that is negative.
Inventors: |
Park; Jung Chul (Pleasanton,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Park; Jung Chul |
Pleasanton |
CA |
US |
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Assignee: |
ASML Masktools B.V. (Veldhoven,
NL)
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Family
ID: |
38870306 |
Appl.
No.: |
13/170,126 |
Filed: |
June 27, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110317908 A1 |
Dec 29, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11898648 |
Sep 13, 2007 |
7970198 |
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60844079 |
Sep 13, 2006 |
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Current U.S.
Class: |
382/144; 382/203;
382/199; 382/276; 382/263; 382/261; 382/145; 382/264; 382/260;
382/190 |
Current CPC
Class: |
G03F
1/70 (20130101) |
Current International
Class: |
G06K
9/00 (20060101) |
Field of
Search: |
;382/144-145 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Thirugnanam; Gandi
Attorney, Agent or Firm: Pillsbury Winthrop Shaw Pittman
LLP
Parent Case Text
RELATED APPLICATIONS
This application is a divisional of U.S. patent application Ser.
No. 11/898,648, filed on Sep. 13, 2007, issued as U.S. Pat. No.
7,970,198, which claims priority to U.S. Patent Application Ser.
No. 60/844,079, filed on Sep. 13, 2006, both of which are
incorporated by reference herein in their entirety.
Claims
What is claimed is:
1. A method for decomposing a target pattern, containing features
to be printed on a wafer, into multiple patterns, wherein processes
utilized to image the target pattern have a minimum pitch, the
method comprising the steps of: (a) defining a first kernel for use
in the decomposing, the first kernel representing a function having
a first value having a first sign at a center, and a second value
having a second sign which is a sign opposite to the first sign at
a distance more than a first distance from the center and less than
a second distance from the center, wherein the first distance
corresponds to a minimum printable critical dimension of the
features, and wherein the second distance corresponds to the
minimum pitch; (b) defining the features utilizing a plurality of
pixels; (c) disposing the first kernel over a pixel of the
plurality of pixels, such that the center of the first kernel is
located on the pixel if a value stored for the pixel has the first
sign, and, disposing a second kernel in which the first and second
signs of the first and second values are reversed with respect to
the first kernel over the pixel, such that the center of the second
kernel is located on the pixel if the value stored for the pixel
has the second sign; (d) determining the first value or the second
value of the disposed kernel at the corresponding location of the
pixel and for adjacent ones of the plurality of pixels that are
located between the first distance and the second distance from the
pixel; (e) storing a value for the pixel and each of the adjacent
ones of the plurality of pixels by adding a previously stored pixel
value to the value determined in step (d); (f) repeating steps
(c)-(e) until each of the plurality of pixels has been processed;
and (g) assigning a pattern formed by pixels of which the stored
pixel value has the first sign to a first pattern, and assigning a
pattern formed by pixels of which the stored pixel value has the
second sign to a second pattern.
2. The method of claim 1, wherein the first kernel is moved
sequentially from one pixel to another pixel of the plurality of
pixels.
3. The method of claim 2, wherein the respective signs of the first
value and the second value of the first kernel are reversed to
generate the second kernel if the value stored for the pixel over
which the center of the first kernel has moved to has the second
sign.
4. The method of claim 1, wherein the first kernel comprises an
annular cross section with the first value with the first sign
within an inner radius and the second value with the second sign
between the inner radius and an outer radius.
5. The method of claim 4, wherein the inner radius corresponds to
the minimum printable critical dimension of the features, and the
outer radius corresponds to the minimum pitch.
6. The method of claim 1 wherein an initial value of each pixel of
the plurality of pixels is set to zero before disposing the first
kernel.
7. A non-transitory computer-readable storage medium storing a
computer program product for decomposing a target pattern,
containing features to be printed on a wafer, into multiple
patterns, wherein processes utilized to image the target pattern
have a minimum pitch, the computer program, when executed, causing
a computer to perform the steps of: (a) defining a first kernel for
use in the decomposing, the first kernel representing a function
having a first value having a first sign at a center, and a second
value having a second sign which is a sign opposite to the first
sign at a distance more than a first distance from the center and
less than a second distance from the center, wherein the first
distance corresponds to a minimum printable critical dimension of
the features, and wherein the second distance corresponds to the
minimum pitch; (b) defining the features utilizing a plurality of
pixels; (c) disposing the first kernel over a pixel of the
plurality of pixels, such that the center of the first kernel is
located on the pixel if a value stored for the pixel has the first
sign, and, disposing a second kernel in which the first and second
signs of the first and second values are reversed with respect to
the first kernel over the pixel, such that the center of the second
kernel is located on the pixel if the value stored for the pixel
has the second sign; (d) determining the first value or the second
value of the disposed kernel at the corresponding location of the
pixel and for adjacent ones of the plurality of pixels that are
located between the first distance and the second distance from the
pixel; (e) storing a value for the pixel and each of the adjacent
ones of the plurality of pixels by adding a previously stored pixel
value to the value determined in step (d); (f) repeating steps
(c)-(e) until each of the plurality of pixels has been processed;
and (g) assigning a pattern formed by pixels of which the stored
pixel value has the first sign to a first pattern, and assigning a
pattern formed by pixels of which the stored pixel value has the
second sign to a second pattern.
8. The computer program product of claim 7, wherein the first
kernel is moved sequentially from one pixel to another pixel of the
plurality of pixels.
9. The computer program product of claim 8, wherein the respective
signs of the first value and the second value of the first kernel
are reversed to generate the second kernel if the value stored for
the pixel over which the center of the first kernel has moved to
has the second sign.
10. The computer program product of claim 7, wherein the first
kernel comprises an annular cross section with the first value with
the first sign within an inner radius and the second value with the
second sign between the inner radius and an outer radius.
11. The method of claim 10 wherein the inner radius corresponds to
the minimum printable critical dimension of the features, and the
outer radius corresponds to the minimum pitch.
12. The method of claim 7, wherein an initial value of each pixel
of the plurality of pixels is set to zero before disposing the
first kernel.
13. A method for generating masks to be utilized in a
photolithography process, said method comprising the steps of: (a)
defining a first kernel for use in the decomposing, the kernel
representing a function having a first value having a first sign at
a center, and a second value having a second sign which is a sign
opposite to the first sign at a distance more than a first distance
and less than a second distance from the center, wherein the first
distance corresponds to a minimum printable critical dimension of
the features and the second distance corresponds to a minimum pitch
of the photolithography process; (b) defining the features
utilizing a plurality of pixels; (c) disposing the first kernel
over a pixel of the plurality of pixels, such that the center of
the first kernel is located on the pixel if a value stored for the
pixel has the first sign, and, disposing a second kernel in which
the first and second signs of the first and second values are
reversed with respect to the first kernel over the pixel, such that
the center of the second kernel is located on the pixel if the
value stored for the pixel has the second sign; (d) determining the
first value or the second value of the disposed kernel at the
corresponding location of the pixel and for adjacent ones of the
plurality of pixels that are located between the first distance and
the second distance from the pixel; (e) storing a value for the
pixel and each of the adjacent ones of the plurality of pixels by
adding a previously stored pixel value to the value determined in
step (d); (f) repeating steps (c)-(e) until each of the plurality
of pixels has been processed; (g) assigning a pattern formed by
pixels of which the stored pixel value has the first sign to a
first pattern, and assigning a pattern formed by pixels of which
the stored pixel value has the second sign to a second pattern; and
(h) generating a first mask corresponding to the first pattern and
a second mask corresponding to the second pattern.
14. The method of claim 13, wherein the first kernel is moved
sequentially from one pixel to another pixel of the plurality of
pixels.
15. The method of claim 14, wherein the respective signs of the
first value and the second value of the first kernel are reversed
to generate the second kernel if the value stored for the pixel
over which the center of the first kernel has moved to has the
second sign.
16. The method of claim 13, wherein the first kernel comprises an
annular cross section with the first value with the first sign
within an inner radius and the second value with the second sign
between the inner radius and an outer radius.
17. The method of claim 16, wherein the inner radius corresponds to
the minimum printable critical dimension of the features, and the
outer radius corresponds to the minimum pitch.
18. The method of claim 13, wherein an initial value of each pixel
of the plurality of pixels is set to zero before disposing the
first kernel.
Description
TECHNICAL FIELD
The technical field of the present invention relates generally to a
method, program product and apparatus for performing a
decomposition of a target pattern into multiple patterns so as to
allow the target pattern to be imaged utilizing, for example,
multiple masks in a multiple illumination process.
BACKGROUND OF THE INVENTION
Lithographic apparatus can be used, for example, in the manufacture
of integrated circuits (ICs). In such a case, the mask may contain
a circuit pattern corresponding to an individual layer of the IC,
and this pattern can be imaged onto a target portion (e.g.,
comprising one or more dies) on a substrate (silicon wafer) that
has been coated with a layer of radiation-sensitive material
(resist). In general, a single wafer will contain a whole network
of adjacent target portions that are successively irradiated via
the projection system, one at a time. In one type of lithographic
projection apparatus, each target portion is irradiated by exposing
the entire mask pattern onto the target portion in one go; such an
apparatus is commonly referred to as a wafer stepper. In an
alternative apparatus, commonly referred to as a step-and-scan
apparatus, each target portion is irradiated by progressively
scanning the mask pattern under the projection beam in a given
reference direction (the "scanning" direction) while synchronously
scanning the substrate table parallel or anti-parallel to this
direction. Since, in general, the projection system will have a
magnification factor M (generally <1), the speed V at which the
substrate table is scanned will be a factor M times that at which
the mask table is scanned. More information with regard to
lithographic devices as described herein can be gleaned, for
example, from U.S. Pat. No. 6,046,792, incorporated herein by
reference.
In a manufacturing process using a lithographic projection
apparatus, a mask pattern is imaged onto a substrate that is at
least partially covered by a layer of radiation-sensitive material
(resist). Prior to this imaging step, the substrate may undergo
various procedures, such as priming, resist coating and a soft
bake. After exposure, the substrate may be subjected to other
procedures, such as a post-exposure bake (PEB), development, a hard
bake and measurement/inspection of the imaged features. This array
of procedures is used as a basis to pattern an individual layer of
a device, e.g., an IC. Such a patterned layer may then undergo
various processes such as etching, ion-implantation (doping),
metallization, oxidation, chemo-mechanical polishing, etc., all
intended to finish off an individual layer. If several layers are
required, then the whole procedure, or a variant thereof, will have
to be repeated for each new layer. Eventually, an array of devices
will be present on the substrate (wafer). These devices are then
separated from one another by a technique such as dicing or sawing,
whence the individual devices can be mounted on a carrier,
connected to pins, etc. For the sake of simplicity, the projection
system may hereinafter be referred to as the "lens"; however, this
term should be broadly interpreted as encompassing various types of
projection systems, including refractive optics, reflective optics,
and catadioptric systems, for example. The radiation system may
also include components operating according to any of these design
types for directing, shaping or controlling the projection beam of
radiation, and such components may also be referred to below,
collectively or singularly, as a "lens." Further, the lithographic
apparatus may be of a type having two or more substrate tables
(and/or two or more mask tables). In such "multiple stage" devices
the additional tables may be used in parallel, or preparatory steps
may be carried out on one or more tables while one or more other
tables are being used for exposures. Twin stage lithographic
apparatus are described, for example, in U.S. Pat. No. 5,969,441,
incorporated herein by reference.
The photolithographic masks referred to above comprise geometric
patterns corresponding to the circuit components to be integrated
onto a silicon wafer. The patterns used to create such masks are
generated utilizing CAD (computer-aided design) programs, this
process often being referred to as EDA (electronic design
automation). Most CAD programs follow a set of predetermined design
rules in order to create functional masks. These rules are set by
processing and design limitations. For example, design rules define
the space tolerance between circuit devices (such as gates,
capacitors, etc.) or interconnect lines, so as to ensure that the
circuit devices or lines do not interact with one another in an
undesirable way. The design rule limitations are typically referred
to as "critical dimensions" (CD). A critical dimension of a circuit
can be defined as the smallest width of a line or hole or the
smallest space between two lines or two holes. Thus, the CD
determines the overall size and density of the designed
circuit.
Of course, one of the goals in integrated circuit fabrication is to
faithfully reproduce the original circuit design on the wafer (via
the mask). As the critical dimensions of the target patterns become
increasingly smaller, it is becoming increasingly harder to
reproduce the target patterns on the wafer. However, there are
known techniques that allow for a reduction in the minimum CD that
can be imaged or reproduced in a wafer. One such technique is the
double exposure technique wherein features in the target pattern
are imaged in two separate exposures.
For example, one commonly known double exposure technique is
referred to as double-patterning or DPT. This technique allows the
features of a given target pattern to be separated into two
different masks and then imaged separately to form the desired
pattern. Such a technique is typically utilized when the target
features are spaced so closely together that it is not possible to
image the individual features. In such a situation, the target
features are separated into two masks such that all the features on
a given mask are spaced sufficiently apart from one another so that
each feature may be individually imaged. Then, by imaging both
masks in a sequential manner (with the appropriate shielding), it
is possible to obtain the target pattern having the densely spaced
features that could not be properly imaged utilizing a single
mask.
Thus, by separating the target features into two separate masks,
such that the pitch between each of the features on a given mask is
above the resolution capabilities of the imaging system, it is
possible to improve imaging performance. Indeed, the
above-mentioned double exposure techniques allow for a
k.sub.1<0.25. However, problems and limitations still exist with
currently known double exposure techniques.
For example, current decomposition techniques include rule-based
decomposition techniques and model-based decomposition techniques.
Rule-based methods typically require an excessive number of rules
to handle today's increasingly complex designs. More specifically,
with a set of pre-constructed geometric rules, it is possible to
start performing pitch-split decomposition. This entails separating
(also referred to as coloring) the odd and even pitch features into
two separate geometry groups or patterns. Conceptually, this is
straight forward process. However, in an actual IC circuit design,
the local 2-dimensional geometry environment is very complex. As
such, it is often difficult to identify "odd" and "even" pitch
features from any of the localized dense pattern groups. As a
result, the existing rule-based approach causes numerous coloring
conflicts that need additional exceptional rules and/or operator
intervention in order to resolve these conflicts. The need for such
additional rules or operator invention make current rule-based
systems very time consuming and problematic to utilize as often
significant time must be taken to tailor the rule set to the given
target design. Model-based decomposition processes also suffer from
various disadvantages. For example, model-based decomposition
methods can take an exceedingly long period of time to complete the
decomposition process. Further, the model-based methods are also
not immune from the non-resolvable conflict issues, and therefore
can also require operator intervention, which is undesirable.
It is an object of the present invention to overcome such
deficiencies in known rule-based and model-based pattern
decomposition techniques.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention
to overcome the deficiencies of known prior art techniques by
providing a simplified decomposition process that does not require
the generation of an extensive rule-base set, and which is suitable
for use with substantially any target pattern.
In summary, the present invention provides a method for decomposing
a target pattern, containing features to be printed on a wafer,
into multiple patterns.
As explained below in further detail, the process of the present
invention provides numerous advantages over the known decomposition
processes. Most importantly, the process provides for a quick and
efficient method of decomposing the target pattern, and eliminates
the need for the generation of a complicated set of rules to govern
pattern decomposition. In addition, the process allows a given
feature to be segments into multiple portions with the portions
being disposed in separate patterns for imaging.
Additional advantages of the present invention will become apparent
to those skilled in the art from the following detailed description
of exemplary embodiments of the present invention.
Although specific reference may be made in this text to the use of
the invention in the manufacture of ICs, it should be explicitly
understood that the invention has many other possible applications.
For example, it may be employed in the manufacture of integrated
optical systems, guidance and detection patterns for magnetic
domain memories, liquid-crystal display panels, thin-film magnetic
heads, etc. The skilled artisan will appreciate that, in the
context of such alternative applications, any use of the terms
"reticle", "wafer" or "die" in this text should be considered as
being replaced by the more general terms "mask", "substrate" and
"target portion", respectively.
The invention itself, together with further objects and advantages,
can be better understood by reference to the following detailed
description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exemplary flowchart illustrating the decomposition
process of the present invention, which is utilized to decompose a
target pattern into multiple patterns.
FIG. 2 illustrates an exemplary kernel which may be utilized in the
model-based decomposition process set forth in FIG. 1.
FIGS. 3-5e illustrate the decomposition process of the present
invention with respect to an exemplary target pattern.
FIGS. 6-8 illustrate an example of the application of the
decomposition process with respect to a line:space target
pattern.
FIGS. 9 and 10 illustrate other examples of the decomposition
process being applied to target patterns.
FIG. 11 is a block diagram that illustrates a computer system which
can implement illumination optimization according to an embodiment
of the present invention.
FIG. 12 schematically depicts an exemplary lithographic projection
apparatus suitable for use with a mask designed with the aid of the
disclosed concepts.
DETAILED DESCRIPTION OF THE INVENTION
As explained in further detail below, the decomposition process of
present invention first entails defining a function or kernel,
which has a different sign with respect to amplitude between the
center of the kernel and an outer radius of the kernel.
Importantly, the negative amplitude of the kernel should be located
at a distance from the center of the kernel which corresponds to
the pitch to be avoided in the pattern layout. Once the kernel is
defined, as explained below in further detail, the kernel is
sequentially placed on each pixel (the size of which is also
predefined) of the target features, and during each placement of
the kernel, the value of the kernel or function at the each pixel
is added (or subtracted if the kernel value is negative) to the
previous value of the pixel to generate a number value associated
with the given pixel. This process is repeated until the kernel has
been positioned on each pixel of each feature to be imaged. Once
this process is completed, each pixel will have associated
therewith either a positive value, a negative value or a zero
value. As shown in the example below, the positive value pixels and
negative value pixels tend to be grouped together. These positive
and negative values are then utilized to separate/decompose the
target features into a first pattern and a second pattern. More
specifically, the pixels have a positive value are placed in the
first pattern and pixels having a negative value are placed in a
second pattern. The zero valued pixels may be placed in either
pattern.
As noted above, the negative amplitude of the kernel should be
located at a distance from the center of the kernel which
corresponds to the pitch to be avoided in the pattern layout. In
other words, the center of the kernel having a positive value can
be deemed as corresponding to the minimum printable CD of the
features, and distance from the center of the kernel to the
negative value, which corresponds to the pitch to be avoided, can
be deemed the area which is below the minimal acceptable pitch of
the given photolithography process being utilized to image the
target pattern. As such, the resulting pitch in the first and
second patterns will be equal to or greater than the minimal
acceptable pitch. It is noted that the minimum acceptable CD and
minimum acceptable pitch (and the pitch to be avoided) for the
process to be utilized to image the patterns can be determined
utilizing empirical or simulation processes, which are well known
in the art.
FIG. 1 is an exemplary flowchart illustrating a first embodiment of
the present invention. Referring to FIG. 1, the first step (Step
10) in the process is to define the original target pattern to be
decomposed into two or more patterns. In the given example, the
target pattern includes a plurality of L-shaped lines as shown in
FIG. 3.
The next step (Step 12) in the process is to define the kernel or
function to be utilized in the decomposition process. As noted
above, the kernel is a function which has a different sign with
respect to amplitude between the center of the kernel and an outer
radius of the kernel, where the outer radius exhibiting the change
of amplitude corresponds to the pitch to be avoided (i.e., a pitch
which is less than the minimum acceptable pitch). FIG. 2
illustrates an exemplary kernel which can be utilized in the
process. Referring to FIG. 2, the kernel has a center section 21
having a positive function value and an outer section 22 having a
negative function value. As noted, the kernel is selected such that
the outer section 22 is placed at a distance corresponding to the
pitch to be avoided. As also shown, the values of the kernel are
the highest at the center of the kernel and decrease as the
distance from the center increases. It is noted that the shape of
the kernel is not limited to the example shown in FIG. 2. Any
function which has a different sign in amplitude between the center
of the kernel and at a set radius away from the center may be
utilized. Further, it is also possible to have the center of the
kernel exhibit a negative amplitude and have the outer radius
corresponding to the pitch to be avoided exhibit a positive value.
The important criteria being that there is a change of sign in
amplitude between the two locations.
Once the kernel is defined, the next step in the process (Step 14),
is to divide the features of the target pattern into pixels with
proper size according to the design of the data format (e.g.,
GDSII) as shown in FIG. 4. It is noted that the pixel size can
range from as small as the design grid permits to the minimum
design line size (i.e., minimum CD). However, because the coloring
is performed on pixel by pixel basis, if the pixel size is too
small, it may take a longer time to complete the decomposition
process. Alternatively, if the pixel size is too large, the
decomposition process may result in a conflict situation. As such,
the pixel size should be selected such that the features can be
evenly divided. As an example, for a 32 nm CD target design, the
pixel size may be on the order of 20 nm. Once this is accomplished,
the next step (Step 16) entails initializing the value of all
pixels of the target features to zero.
Next, in Step 18, a first pixel is selected. Then, the center of
the kernel is placed/positioned on the first pixel (Step 20), and
the value of the kernel at the corresponding pixel location is
determined for all of the pixels within the diameter of the kernel.
As shown, in FIG. 2, the amplitude value of the kernel changes as
the distance from the center of the kernel increases. Thereafter
(Step 24), the value of the kernel at the given pixel location is
added or subtracted (if the kernel value is negative) to the
current pixel intensity or value (all of which are initially set to
zero) for all of the pixels within the diameter of the kernel. The
process then proceeds to Step 25 where it is determined if the
kernel has been placed on each of the pixels. If the answer is no,
the process proceeds to Step 26 and selects the next pixel and then
repeats Steps 20-25 until all of the pixels have been processed. It
is noted that the value of the pixels is cumulative and is updated
during each reiteration. Once all of the pixels have been
processed, in Step 27 the pixels are separated into either the
first pattern or the second pattern based on whether the value of
the given pixel is positive or negative. The first and second
pattern can then be utilized to form first and second masks, which
may be utilized in the multiple illumination process.
FIGS. 5a-5e illustrate the application of the foregoing
decomposition process to the exemplary target pattern shown in FIG.
3. Initially, the kernel is placed on a first pixel in the upper
corner of the pattern, and the kernel is overlaid on the target
pattern, with the kernel being centered on the first pixel. The
values of all of the pixels within the radius of the kernel
function are updated. Specifically, when the value of the kernel at
the location of the given pixel is position, the kernel value is
added to the pixel value, and when the value of the kernel at the
location of the given pixel is negative, the kernel value is
subtracted from the pixel value. Once this is done, the kernel is
moved to the next pixel and the process is repeated. Referring to
FIGS. 5a-5e, it is shown that as the kernel is shifted over the
pixels forming the target patterns, the features begin to be
decomposed or separated from one another based in-part on the value
of the pitch to be avoided, which is utilized to define the kernel.
Once all of the pixels have been processed, the target pattern is
completely decomposed. While it is not necessary to move the kernel
from pixel-to-pixel in any particular order, in the given example,
the kernel is moved in a raster manner. However, it is also
possible to move the kernel in any other suitable pattern.
It is noted that the both the values of the pixels and the kernel
may be maintained utilizing an x-y coordinate system so as to allow
for ready identification and storage of the values of the pixels
and kernel, as well as for ready placement of the kernel over the
pixels. It is further noted that as a practical matter all pixels
can be updated, however, the pixels outside of the kernel radius
will simply be adding or subtracting a zero value from the current
pixel value.
FIGS. 6-8 illustrate another example of the application of the
decomposition process as applied to a line space pattern. The pixel
values of the respective lines are shown when the kernel is
initially positioned over the leftmost line 602. This can be
thought of as step 1. In FIG. 6, cross section (along the line 612)
of the line patterns 602, 604, 606, 608, and 610 are represented by
pixel groups 603, 605, 607, 609, and 611, respectively. Referring
to the graph 601 of FIG. 6, which represents the kernel intensity
value, the pixel value associated with the first line 602 is
positive, while the pixel value of the second line 604 (immediately
to the right of the leftmost line 602) is negative. Again, as noted
above, this is due to the predefined intensity values of the kernel
which are selected so that features spaced below the minimal
acceptable pitch are placed in separate patterns. FIGS. 7 and 8 are
examples of how the values change as the kernel is shifted from
pixel to pixel. In the left hand side plot in FIG. 7, labeled as
step 2, the group of pixels indicated as 620 represents modified
pixel intensity values for the group 603 when kernel intensity
values are added to the original pixel intensity values. In step 2,
the center of the kernel 601 is superposed on the center of the
pixel group 603. In the right hand side plot in FIG. 7, labeled as
step 3, the kernel 601 has been shifted by one pixel from the
center of the pixel group 603. Further, in step 3, the pixel
intensity value already assigned to the pixel is checked. If the
pixel intensity value is greater than zero (or of a certain
polarity), then kernel intensity value is added to the pixel
intensity value, as in step 2. But, if the pixel intensity value is
less than zero (or of an opposite polarity), then first the
polarity if the kernel intensity value is flipped, and then the
kernel intensity value is added to the pixel intensity value, as in
step 2. The group of pixels indicated as 622 represents modified
pixel intensity values for the group 603 with the kernel 601 is
shifted by one pixel. Steps 2 and 3 are repeated until all the
pixels are covered. The plots in FIG. 8 illustrates the reversal of
polarity (or sign) of the kernel intensity value, as discussed in
step 3 above. In the right hand plot of FIG. 8, it is shown that
when the center of the kernel 601 is shifted to the second line
604, polarity of the kernel is changed. The kernel 602 is the
modified kernel with flipped polarity with respect to kernel 601.
Persons skilled in the art will understand in view of the present
methodology that since the second line 604 has a sum value of
intensity less than zero, flipping of kernel was done, according to
step 3 rules, as discussed before. 624 and 628 represent modified
pixel intensity values corresponding to pixel group 603 (line 602),
and, 626 and 630 represent modified pixel intensity values
corresponding to pixel group 605 (line 604).
Finally, FIG. 9 illustrates the result of the decomposition process
being applied to an elbow pattern. The result, which is the same as
shown in FIG. 5e, is that the pattern is decomposed into patterns,
the first pattern including features 91 and the second pattern
including features 93. FIG. 10 illustrates the result of the
decomposition process being applied to a line space pattern having
densely spaced features 101 and 103 and non-dense features 1020. As
shown, the result is that the densely spaced features (i.e.,
features 101 and 103) are separated into separate patterns, while
the non-densely spaced patterns are left unchanged.
As detailed above, the process of the present invention provides
numerous advantages over the known decomposition processes. Most
importantly, the process provides for a quick and efficient method
of decomposing the target pattern, and eliminates the need for the
generation of a complicated set of rules to govern pattern
decomposition.
Variations of the exemplary process detailed above are also
possible. For example, it is possible to apply optical proximity
correction treatments to the decomposed patterns resulting from the
process of the present invention. Further, either rule-based or
model-based OPC treatments may be utilized on the decomposed
patterns.
In yet another variation, different functions, other than the one
disclosed above, may be utilized to represent the kernel in the
decomposition process. Again, the important aspect is that the
function have a different sign in amplitude between the center of
the function and the radius corresponding to the undesirable pitch,
which is to be avoided.
FIG. 11 is a block diagram that illustrates a computer system 100
which can implement the pattern decomposition process detailed
above. Computer system 100 includes a bus 102 or other
communication mechanism for communicating information, and a
processor 104 coupled with bus 102 for processing information.
Computer system 100 also includes a main memory 106, such as a
random access memory (RAM) or other dynamic storage device, coupled
to bus 102 for storing information and instructions to be executed
by processor 104. Main memory 106 also may be used for storing
temporary variables or other intermediate information during
execution of instructions to be executed by processor 104.
Computer system 100 further includes a read only memory (ROM) 108
or other static storage device coupled to bus 102 for storing
static information and instructions for processor 104. A storage
device 110, such as a magnetic disk or optical disk, is provided
and coupled to bus 102 for storing information and
instructions.
Computer system 100 may be coupled via bus 102 to a display 112,
such as a cathode ray tube (CRT) or flat panel or touch panel
display for displaying information to a computer user. An input
device 114, including alphanumeric and other keys, is coupled to
bus 102 for communicating information and command selections to
processor 104. Another type of user input device is cursor control
116, such as a mouse, a trackball, or cursor direction keys for
communicating direction information and command selections to
processor 104 and for controlling cursor movement on display 112.
This input device typically has two degrees of freedom in two axes,
a first axis (e.g., x) and a second axis (e.g., y), that allows the
device to specify positions in a plane. A touch panel (screen)
display may also be used as an input device.
According to one embodiment of the invention, the coloring process
may be performed by computer system 100 in response to processor
104 executing one or more sequences of one or more instructions
contained in main memory 106. Such instructions may be read into
main memory 106 from another computer-readable medium, such as
storage device 110. Execution of the sequences of instructions
contained in main memory 106 causes processor 104 to perform the
process steps described herein. One or more processors in a
multi-processing arrangement may also be employed to execute the
sequences of instructions contained in main memory 106. In
alternative embodiments, hard-wired circuitry may be used in place
of or in combination with software instructions to implement the
invention. Thus, embodiments of the invention are not limited to
any specific combination of hardware circuitry and software.
The term "computer-readable medium" as used herein refers to any
medium that participates in providing instructions to processor 104
for execution. Such a medium may take many forms, including but not
limited to, non-volatile media, volatile media, and transmission
media. Non-volatile media include, for example, optical or magnetic
disks, such as storage device 110. Volatile media include dynamic
memory, such as main memory 106. Transmission media include coaxial
cables, copper wire and fiber optics, including the wires that
comprise bus 102. Transmission media can also take the form of
acoustic or light waves, such as those generated during radio
frequency (RF) and infrared (IR) data communications. Common forms
of computer-readable media include, for example, a floppy disk, a
flexible disk, hard disk, magnetic tape, any other magnetic medium,
a CD-ROM, DVD, any other optical medium, punch cards, paper tape,
any other physical medium with patterns of holes, a RAM, a PROM,
and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a
carrier wave as described hereinafter, or any other medium from
which a computer can read.
Various forms of computer readable media may be involved in
carrying one or more sequences of one or more instructions to
processor 104 for execution. For example, the instructions may
initially be borne on a magnetic disk of a remote computer. The
remote computer can load the instructions into its dynamic memory
and send the instructions over a telephone line using a modem. A
modem local to computer system 100 can receive the data on the
telephone line and use an infrared transmitter to convert the data
to an infrared signal. An infrared detector coupled to bus 102 can
receive the data carried in the infrared signal and place the data
on bus 102. Bus 102 carries the data to main memory 106, from which
processor 104 retrieves and executes the instructions. The
instructions received by main memory 106 may optionally be stored
on storage device 110 either before or after execution by processor
104.
Computer system 100 also preferably includes a communication
interface 118 coupled to bus 102. Communication interface 118
provides a two-way data communication coupling to a network link
120 that is connected to a local network 122. For example,
communication interface 118 may be an integrated services digital
network (ISDN) card or a modem to provide a data communication
connection to a corresponding type of telephone line. As another
example, communication interface 118 may be a local area network
(LAN) card to provide a data communication connection to a
compatible LAN. Wireless links may also be implemented. In any such
implementation, communication interface 118 sends and receives
electrical, electromagnetic or optical signals that carry digital
data streams representing various types of information.
Network link 120 typically provides data communication through one
or more networks to other data devices. For example, network link
120 may provide a connection through local network 122 to a host
computer 124 or to data equipment operated by an Internet Service
Provider (ISP) 126. ISP 126 in turn provides data communication
services through the worldwide packet data communication network,
now commonly referred to as the "Internet" 128. Local network 122
and Internet 128 both use electrical, electromagnetic or optical
signals that carry digital data streams. The signals through the
various networks and the signals on network link 120 and through
communication interface 118, which carry the digital data to and
from computer system 100, are exemplary forms of carrier waves
transporting the information.
Computer system 100 can send messages and receive data, including
program code, through the network(s), network link 120, and
communication interface 118. In the Internet example, a server 130
might transmit a requested code for an application program through
Internet 128, ISP 126, local network 122 and communication
interface 118. In accordance with the invention, one such
downloaded application provides for the illumination optimization
of the embodiment, for example. The received code may be executed
by processor 104 as it is received, and/or stored in storage device
110, or other non-volatile storage for later execution. In this
manner, computer system 100 may obtain application code in the form
of a carrier wave.
FIG. 12 schematically depicts a lithographic projection apparatus
suitable for use with a mask designed with the aid of the current
invention. The apparatus comprises: a radiation system Ex, IL, for
supplying a projection beam PB of radiation. In this particular
case, the radiation system also comprises a radiation source LA; a
first object table (mask table) MT provided with a mask holder for
holding a mask MA (e.g., a reticle), and connected to first
positioning means for accurately positioning the mask with respect
to item PL; a second object table (substrate table) WT provided
with a substrate holder for holding a substrate W (e.g., a
resist-coated silicon wafer), and connected to second positioning
means for accurately positioning the substrate with respect to item
PL; a projection system ("lens") PL (e.g., a refractive, catoptric
or catadioptric optical system) for imaging an irradiated portion
of the mask MA onto a target portion C (e.g., comprising one or
more dies) of the substrate W.
As depicted herein, the apparatus is of a transmissive type (i.e.,
has a transmissive mask). However, in general, it may also be of a
reflective type, for example (with a reflective mask).
Alternatively, the apparatus may employ another kind of patterning
means as an alternative to the use of a mask; examples include a
programmable mirror array or LCD matrix.
The source LA (e.g., a mercury lamp or excimer laser) produces a
beam of radiation. This beam is fed into an illumination system
(illuminator) IL, either directly or after having traversed
conditioning means, such as a beam expander Ex, for example. The
illuminator IL may comprise adjusting means AM for setting the
outer and/or inner radial extent (commonly referred to as
.sigma.-outer and .sigma.-inner, respectively) of the intensity
distribution in the beam. In addition, it will generally comprise
various other components, such as an integrator IN and a condenser
CO. In this way, the beam PB impinging on the mask MA has a desired
uniformity and intensity distribution in its cross-section.
It should be noted with regard to FIG. 12 that the source LA may be
within the housing of the lithographic projection apparatus (as is
often the case when the source LA is a mercury lamp, for example),
but that it may also be remote from the lithographic projection
apparatus, the radiation beam that it produces being led into the
apparatus (e.g., with the aid of suitable directing mirrors); this
latter scenario is often the case when the source LA is an excimer
laser (e.g., based on KrF, ArF or F.sub.2 lasing). The current
invention encompasses both of these scenarios.
The beam PB subsequently intercepts the mask MA, which is held on a
mask table MT. Having traversed the mask MA, the beam PB passes
through the lens PL, which focuses the beam PB onto a target
portion C of the substrate W. With the aid of the second
positioning means (and interferometric measuring means IF), the
substrate table WT can be moved accurately, e.g., so as to position
different target portions C in the path of the beam PB. Similarly,
the first positioning means can be used to accurately position the
mask MA with respect to the path of the beam PB, e.g., after
mechanical retrieval of the mask MA from a mask library, or during
a scan. In general, movement of the object tables MT, WT will be
realized with the aid of a long-stroke module (coarse positioning)
and a short-stroke module (fine positioning), which are not
explicitly depicted in FIG. 12. However, in the case of a wafer
stepper (as opposed to a step-and-scan tool) the mask table MT may
just be connected to a short-stroke actuator, or may be fixed.
The depicted tool can be used in two different modes: In step mode,
the mask table MT is kept essentially stationary, and an entire
mask image is projected in one go (i.e., a single "flash") onto a
target portion C. The substrate table WT is then shifted in the x
and/or y directions so that a different target portion C can be
irradiated by the beam PB; In scan mode, essentially the same
scenario applies, except that a given target portion C is not
exposed in a single "flash". Instead, the mask table MT is movable
in a given direction (the so-called "scan direction", e.g., the y
direction) with a speed v, so that the projection beam PB is caused
to scan over a mask image; concurrently, the substrate table WT is
simultaneously moved in the same or opposite direction at a speed
V=Mv, in which M is the magnification of the lens PL (typically,
M=1/4 or 1/5). In this manner, a relatively large target portion C
can be exposed, without having to compromise on resolution.
Additionally, software may implement or aid in performing the
disclosed concepts. Software functionalities of a computer system
involve programming, including executable code, may be used to
implement the above described imaging model. The software code is
executable by the general-purpose computer. In operation, the code,
and possibly the associated data records, are stored within a
general-purpose computer platform. At other times, however, the
software may be stored at other locations and/or transported for
loading into the appropriate general-purpose computer systems.
Hence, the embodiments discussed above involve one or more software
products in the form of one or more modules of code carried by at
least one machine-readable medium. Execution of such code by a
processor of the computer system enables the platform to implement
the catalog and/or software downloading functions in essentially
the manner performed in the embodiments discussed and illustrated
herein.
As used herein, terms such as computer or machine "readable medium"
refer to any medium that participates in providing instructions to
a processor for execution. Such a medium may take many forms,
including but not limited to, non-volatile media, volatile media,
and transmission media. Non-volatile media include, for example,
optical or magnetic disks, such as any of the storage devices in
any computer(s) operating as one of the server platforms discussed
above. Volatile media include dynamic memory, such as main memory
of such a computer platform. Physical transmission media include
coaxial cables, copper wire and fiber optics, including the wires
that comprise a bus within a computer system. Carrier-wave
transmission media can take the form of electric or electromagnetic
signals, or acoustic or light waves such as those generated during
radio frequency (RF) and infrared (IR) data communications. Common
forms of computer-readable media therefore include, for example: a
floppy disk, a flexible disk, hard disk, magnetic tape, any other
magnetic medium, a CD-ROM, DVD, any other optical medium, less
commonly used media such as punch cards, paper tape, any other
physical medium with patterns of holes, a RAM, a PROM, and EPROM, a
FLASH-EPROM, any other memory chip or cartridge, a carrier wave
transporting data or instructions, cables or links transporting
such a carrier wave, or any other medium from which a computer can
read programming code and/or data. Many of these forms of computer
readable media may be involved in carrying one or more sequences of
one or more instructions to a processor for execution.
Although the present invention has been described and illustrated
in detail, it is to be clearly understood that the same is by way
of illustration and example only and is not to be taken by way of
limitation, the scope of the present invention being limited only
by the terms of the appended claims.
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